Apparatus for purifying pulp stock



Sept. 25, 1934. s C UNDBERG 1,974,679

APPARATUS FOR PURIFYING PULP STOCK Filed Sept. 3, 1930 2 Sheets-Sheet l Sept. 25, 1934. s. c. LINDBERG APPARATUS FOR PURIFYING PULP STOCK Filed Sept. 3, 1950 2 Sheets-Sheet 2 Jaw zf'wz dfzmi Patented Sept. 25, 1934 UNITED STATES [PATENT OFFICE Sven O. Lindberg, New

York, N. Y., assignor, by

mesne assignments, to Centrifugal Engineering and Patents Corporation, New York, N. Y., a corporation of New Jersey Application September 3, 1930, Serial No. 479,496 I 3 Claims.

This invention relates to a method of and apparatus for separating bits of dirt or foreign matter from pulp stock. In the manufacture of the better grade of papers and other materials and articles in which cellulosic pulp is used as a constituent it is desirable to provide pulp stock which is as free as possible from all foreign matter. The type of dirt or, foreign matter liable to occur in pulp stock varies with the source of the pulp. For example, pulp made 'from rags is liable to contain bits of rubber, fragmentsjof buttons, ordinary dirt and such other impurities as may be found in or with rags. Most of this matter can;

be separated from the pulp -by-fiowing pulp through a centrifuge, such, for example, as is described and illustrated in application Serial No. 388,704, filed August 27, 1929, since the difference in specific gravity between the pulp fibers and the impuritiescause the latter to separate out -under the centrifugal action of the rotating drum.

The problem of purifying wood pulp is somewhat difiicult owing to the frequent occurrence of such impurities as slivers of bark, knots or uncooked fiber. Impurities of this kind have a specific gravity almost identical with the pulp fiber so that they are not as readily separated out as are particles having a greater or lesser specific gravity. The apparatus herein described is more particularly designed for use in purifying wood pulp. To this end a centrifuge is provided, the proportions and dimensions of which are particularly adapted for handling such material. Since the specific gravity of the slivers usually found in wood pulp is little, if any, different from the specific gravity of the pulp fibers, advantage must be taken of the difference in size of the particles. The slivers are usually larger than the pulp fibers so that their inertia is greater. This fact is utilized in designing a centrifuge embodying the present invention. According to this invention a centrifuge is provided having a series of compartments therein formed by annular baffies or ribs extending inwardly from the shell of the drum. The diameters of the inner edges of these ribs are substantially different so that the pools of pulp formed in the several compartments within the drum have successively greater-surface diameters, the difference between successive diameters being substantial and as great as limitations of structure and operation will permit.

The operation of a centrifuge of the general type illustrated on the drawing and in said application hereinbefore referred to is as follows: The centrifuge may be mounted to revolve on a horizontal, vertical, or sloping axis. For convenience, the following description is in terms of a centrifuge revolving on a vertical axis. The pulp stock to be refined is introduced into the lowermost compartment of the centrifuge. When the centrifuge is first started up, the initial pulp gathers in a pool in this compartment until it overflows the upper rib or baflle defining the compartment. The pulp thereupon flows continuously over the edge of this baflle until' a second pool is formed in an adjoining compartment, this pool overflowing as before into the next compartment until the top of the centrifuge is reached. The pulp is discharged in a continu-' ou's'fstream over the upper rim of the centrifuge and is" caught by a suitable gutter extending around this rim. In each of the compartments in the drum the pulp forms a soft mat over which the pulp stream fiows, which mat of pulp fibers combs the pulp in the flowing stream and tends to catch and remove from the stream the slivers and particles of foreign matter therein. If, however, the slivers or foreign matter have a specific gravity substantially equal to that of the fibers, they are not so readily caught as are the particles of heavier material. When there is a considerable drop from the surface of one pool to the surface of the pool in the adjoining compartment, it is found that a considerable proportion of the slivers are caught in the pulp matof the second compartment at the point where the pulp stream enters from the first compartment by flowing over the baffle or rib between them. The greater the diiference of diameter between the successive pools, the more efficient is the separation of the slivers from the pulp stream. This is doubtless due to the difference in linear speed of the two pools of pulp in the compartments. :Particles of pulp leaving the pool of smaller diameter tend to travel in a direction tangent to the surface of this pool and at a velocity substantially equal to the velocity at the surface of the pool. The particles of pulp thus escaping from the pool of smaller diameter travel until they meet the surface of the next adjacent pool which is of substantially larger surface diameter. Since the angular speed of both pools is the same, the linear speed of the second pool will be considerably greater than the speed of the particles entering it, so that the particles enter the second pool at an angle to its surface and are at once accelerated thereby.

If a particle has greater inertia than the average fiber in the pulp, the tendency is for this inertia to cause the particles to enter more deeply into the pulp mat of the second pool since it does not so readily acquire the additional velocity of the second pool. Hence, the slivers of bark, etc. pass from the first pool to the second and tend to penetrate more deeply into the pulp mat of the second pool than do the average fibers of the pulp stream. In this way advantage is taken of the particle size of the slivers to remove them from the pulp stream. In order to make the process more effective, a number of such substantial drops between successive pools may be provided so as to produce a final product which is substantially free from slivers of any kind as well as from other impurities.

In operating a centrifuge of the type described, it has been customary to run a centrifuge for a given number of hours until the dirt collecting capacity of the machine is exhausted and then stopping the machine to clean it out. The period of operation during which a machine can be run with efficient purification of the pulp depends on both the structure of the machine and more especially on the type of pulp to be purified. The ordinary period of operation can be extended in certain ways such as by occasionally running through the centrifuge a stream of thicker pulp. This forms a fresh surface layer on the pulp mats in the pool, the original mats being compressed to a greater density. The fresh mats offer clean surfaces to catch the dirt from the pulp stream. This method of temporarily renewing the cleansing efiiciency of the centrifuge is open to objection, since it varies the consistency of the product issuing from the machine.

It is also often inconvenient to supply pulp of different consistencies.

According to the present invention mechanism is provided by which the operation of the centrifuge may be made substantially continuous; To this end each compartment of the centrifuge is provided with suitable radial outlets in'the form of slots, holes or other passages extending through the wall of the centrifuge and normally closed by movable closure elements. These elements may be in the form of stoppers to enter the holes or slots or they may be in the form of gates which slide across the openings, or any other suitable, equivalent. In using an apparatus of this kind the gates are opened at sufficiently frequent intervals to allow the pulp impurities in the compartments to drain outwardly through the wall of the centrifuge before the mats have become too compact to flow readily. This discharge of the mats is materially aided by the centrifugal action of the rotation of the pools. Thus the centrifuges may be cleaned at frequent intervals with scarcely any interruption in their operation. This is particularly advantageous in the purifying of unbeaten wood pulp fibers. When operating with such material a centrifuge usually begins to lose its purifying efficiency within two or three hours. It is obvious, however, that the draining mechanism can also be used to advantage on centrifuges in which other types of pulp are being purified.

For a more complete understanding of the invention, reference may be had to certain embodiments thereof hereinafter described in detail and illustrated on the drawings, of which,-

Figure 1 is a side elevation, partly in section, of mechanism embodying the invention.

Figure 2 is a section on the line 22 of Figure 1.

Figure 3 is a sectional detail of Figure 1 as shown by a larger scale.

Figure 4 is a similar sectional detail illustrating a modified form of the invention.

Figure 5 is a section on the line 5-5 of Figure 3.

Figure 6 is a sectional view of a modified embodiment of the invention.

Figure 7 is a partial section taken on the line '7'7 of Figure 6.

Figure 8 is a section on the line 88 of Figure 6.

Figure 9 is a sectional detail of a portion of Figure 6, on a larger scale.

The mechanism illustrated in Figure 1 includes a pair of rotatable drums 11 and 12 which may be mounted on a common shaft 13 driven by a suitable motor 14. As shown, the drums are rotatable on a vertical axis, but they may, if desired, be mounted to rotate on a horizontal axis. The drums, as shown, are substantially identical in structure so that a description of one will suflice for both. Referring to the upper drum 11, it is preferably constructed in a frustoconical shape. Mounted within the drum are a series of annular ribs or baffles 15 and 16 which extend inwardly from the inner surface of the drum 11. It is obvious that a larger or smaller number of such ribs may be supplied. It is desirable, according to the invention, that the inner diameters of these ribs be substantially different since these diameters determine the surfaces of pools of pulp which are formed within the circumferential compartments defined by the ribs. Since the shell of the drum l1 tapers, the ribs 15 and 16 may be of substantially the same width, the taper of the drum resulting in the rib 15 having a substantially smaller diameter than the rib 16. An inwardly extending rim or lip 17 may be formed or mounted at the upper end of the drum, the inner diameter of the rim 1? being greater than that of the rib 16, so that the surface of the pool against the rim 17 has a considerably larger diameter than that of the pool against the rib 16. At the lower end of the drum is mounted a bottom plate 18 which has large annular openings as at 19 for washing out the drum. At the upper end of the drum a skimming ring 21 may be mounted, this ring having a lip 22 submerged beneath the surface of the uppermost pool so as to catch any impurities of low specific gravity which may float on the surface of this pool. The pulp which is discharged over the rim 17 may be caught by a suitable gutter 23 which encircles the upper portion of the drum, this gutter being mounted on a conical casing 24 which, in turn, may be supported by a suitable framework 25. One or more manholes 26 may be supplied in the top of the housing to permit access to the interior of the casing in cleaning or for repairs.

The stream of pulp to be purified may be introduced in any convenient manner, as by a supply pipe 27 leading into the top of the housing and extending downwardly into the drum to a point below the rib 15. The discharge end of the pipe 27 may be supplied with a nozzle 28 directed in such a way as to discharge the stream of pulp substantially tangent to and in the same direction as the movement of rotation of the drum so that the pulp is thus introduced into the drum with a minimum disturbance. The pulp first entering from the supply pipe 27 forms in a pool below the rib 15, downward flow being prevented by the bottom plate 18. The rotation of the drum is sufiicient to maintain the pool with a nearly cylindrical surface. when 15 the circumferential compartment below the rib 15 is filled by the pool, there is thereafter an overflow intothe compartment between the ribs 15 and 16. A pool is formed in this compartment having a materially greater surface diameter than that of the pool below the compartment 15, so that the linear speed of the second pool is considerably greater than that of thefirst pool. In like manner a third pool is formed between the rib 16 and the upper rim 17, this pool having a larger surface diameter than either of the lower pools, Particles of pulp flowing from any pool into the'pool above enter that pool at an angle to its surface and are at once accelerated thereby. Thus particles of larger than average size tend to penetrate into the pulp mat formed in the pool and are thus entrapped thereby. While it is desirable that the difference of surface diameter between successive pools be as great as possible, there is a practical limit to these differences owing to the fact that there should not be too great a difference in diameter between the uppermost and lowermost pools, since the greater the diameter the more rapidly is the pulp in the pool compacted. If the pulp mat in any pool becomes compacted beyond a certain density it loses its efficiency in catching and retaining impurities from the pulp stream.

In order to provide additional space between successive pools, the pulp discharged from the top of the drum 11 may be runthrough the drum 12 and if desired through additional drums. To

' this end a discharge pipe may be connected.

with the receiving gutter 23, this pipe 30 extending downwardly into the lower portion of the drum 12 and discharging thereinto through a suitable nozzle 31. His identical with that ofthe drum 11, the additional clearance space being-merely to catch steps.

For some types of pulp suspensions, it maybe preferable to include all the successive ribs and pools in a single drum, as, for example, that shown in Figure 6, in which embodiment a single tapering drum 35 is mounted on a suitable shaft 36 and driven by a motor 37 or equivalent power connection. The pulp stream may be supplied through a suitable pipe 38 which, as shown, empties into a central cylinder 40 which rotates with the shaft 36 and extends downwardly to the lower end of the drum 35. The pulp is discharged through openings 41 from the cylinder 40 into the lower end portion of the drum. Within the drum are a series of annular baffles or ribs 42, nine such ribs being illustrated. These ribs may extend equal distances in from the conical surface of the drum so that their inner diameters are successively greater from the lower rib to the uppermost. Thus when pulp is flowed through the particles that have been missed-bythe previous j rotating drum, a series of pools is formed, each pool having a larger surface diameter than the one below it. Hence a large number oteffective cleaning steps are provided for the rergiolal of silvers of various kinds from the pulp i e manner hereinbefore described. The uppermost pool may be maintained below a rim 43 at the upper end of the drum and a suitable skimming ring 44 may also be provided. The drum may be surrounded by a housing 45 including a channel 46 in which the pulp stream is caught after it escapes over the rim 43 of the drum and is conducted ofi, as by a discharge pipe 47.

In order to avoid the necessity of frequent shutdowns for the purpose of cleaning out the pulp The operation of the drum.

mats in the pools soon after they have accumulated all the dirt or foreign matter they can hold, I may provide a mechanism by which the mats may be quickly and easily discharged from the several pools without stopping or slowing down the drum. To this end suitable passages or apertures 50 may be formed througn the drum (as shown in Figure 3) to permit the escape of pulp from the pools outwardly into the interior of the casing 24. These passages are normally closed by any suitable closure elements, such, for example; as the slides 51 illustrated in Figure 3, or the plugs 52 illustrated in Figure 4. The slides 51 may be held slidably against the outer surface of the drum by suitable guides similar to those illustrated in Figure 8. Each of the slides 51 may be connected, as by a link 53, with a lever 54 pivotally mounted on an ear 55 projecting from the drum 11. At the outer end of the lever 54 is a suitable weight 56. The effect of the rotation of the drum is to cause the weights 56 to pull horizontally outward from the rocking axis of the lever 54. This tends to maintain the slides 51 in their operative position shown in Figure 3,

wherein they effectively close the passages 50. 100.

For the efficient discharge of the pulp mats, a considerable number of passages 50 may be provided for each of the pools of the stream. These track 61 which is supported by a series of plungers 62 extending through the bottom 63 of the housing 24. The plungers 62 are all carried by a spider 64 which can be raised or lowered by a suitable lever 65. It is apparent that if the handle of the lever 65 is depressed the track 61 will be elevated, thus pushing the connecting rods 57 upwardly. This rocks all of the levers 54 and opens all of the passages 50 permitting the discharge of pulp therethrough from the several compartments in the drum. When the operating lever 65 is released, centrifugal action of the weights 56 causes the slides 51 to close the passages 50 and fresh pools in the drum are thereupon formed. The pulp discharged through the openings 50 is caught by the housing 24 and may be eventually discharged through a drain pipe 66.

Somewhat similar apparatus may be used for operating the plugs 52, as illustrated in Figure 4. As shown, each plug is attached to a three arm bell crank '10, one arm of the bell crank carrying a weight 71 which is arranged to press the plug 52 into its aperture by the centrifugal force acting on the weight. The several bell cranks in each 1 5 vertical series may be connected as by connecting rods 5'7, the actuation of the rods being similar to that described in connection with the slides shown in Figure 3.

Instead of individual slides 51 for each of the apertures 50, I may provide elongated strips '72, as shown in Figures 6 and 9, these strips being adapted to fit over. corresponding vertical series of passages 50. Each strip has a series of holes '73 therethrough so spaced that they mayall be simultaneously in registry with the passages 50 normally closed by the strip. The strip may be held slidably against the surface of the drum as by a suitable number of guide members 74 secured to the outer face of the drum. Each strip 72 may 15 be connected as by a connecting rod 75 to a lever 76 pivoted as at 77 to the lower end of the drum. The lever 76 normally extends horizontally outward from its pivot and is provided with a weight 78 mounted at its lower end. The lever '76 also has a downwardly extending arm 80 carrying a roller 81 which may ride on a circular track 82. The track is carried by a suitable spider 83 and can be raised by the operating lever 84 so as to rock all of the levers 76 upwardly and thus to slide the strips '72 so as to open all the passages 50 simultaneously for the discharge of the pulp mats from the successive pools.

It is obvious that many modifications and changes may be made in the apparatus illustrated without departing from the spirit and scope of the invention.

I claim:

1. Apparatus for purifying paper pulp stock comprising a rotatable drum, and means for draining said drum during rotation thereof, said draining means including a passage extending outwardly through the wall of said drum, 9. closure element for said passage, means operable by centrifugal force of rotation to hold said closure element in operative position during rotation of said drum, and means manually operable during the rotation of the drum to move said closure element against said force to open said passage.

2. Apparatus for purifying paper pulp stock comprising a rotatable drum, annular ribs projecting inwardly from the inner surface of said drum to form circumferential compartments therein, and means for draining said compartments during the rotation of said drum, said draining means including passages extending outwardly from said compartments through the drum wall, closure elements for said passages, centrifugal means actuated by rotation of the drum to move said closure elements to close said passages, and manually operable means for moving said closure elements against the force of said centrifugal means to open said passages.

3. Apparatus for purifying paper pulp stock, which comprises a rotatable drum having interior annular ribs, said drum and ribs being arranged to maintain during the rotation of the drum a series of pools of stock at successively increasing radial distances from the axis of rotation, said drum having apertures through the wall thereof adapted to permit the escape of stock centrifugally from each of said pools, closure means operable both by gravitational force and by centrifugal force to close said apertures, and means manually operable when the drum is rotating or at rest for moving said closure means against said forces to open said apertures.

SVEN C. LINDBERG. 

